Source note · Call transfer semantics REFER and Replaces

Proxy servers require no new behaviour to support Replaces and simply pass the header field transparently, and RFC 3891 notes that a proxy forking on application logic such as caller screening or time-of-day routing can forward a Replaces INVITE to a completely different set of contacts from the request it was meant to replace, in which case the request fails.

Checked 2026-09-16

Vendor: IETF
Product: Session Initiation Protocol
Subsystem: Replaces
Deployment: not restricted
Region: not restricted
Release range: Standards Track
Checked: 2026-09-16

Sources

RFC 3891 — The Session Initiation Protocol (SIP) "Replaces" Header — IETF / RFC Editor · tier 1 standards and regulators · RFC 3891 section 5 Proxy behavior

Cite this note

APA

WarmTransfer. (2026, September 16). Call transfer semantics REFER and Replaces: source note xfersem-replaces-proxies-can-break-it. WarmTransfer. https://warmtransfer.net/knowledge/claims/xfersem-replaces-proxies-can-break-it

BibTeX

@misc{warmtransfer-claim-xfersem-replaces-proxies-can-break-it,
  title  = {Call transfer semantics REFER and Replaces: source note xfersem-replaces-proxies-can-break-it},
  author = {{WarmTransfer}},
  year   = {2026},
  url    = {https://warmtransfer.net/knowledge/claims/xfersem-replaces-proxies-can-break-it},
  note   = {Source note xfersem-replaces-proxies-can-break-it, checked 2026-09-16}
}

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